1. Field of the Invention
This invention generally relates to systems and methods for driving piezoelectric transducers. More specifically, this invention relates to a method for damping residual vibrations of a piezoelectric transducer after excitation.
2. Description of the Related Art
Many measuring techniques and devices require an accurate measurement of the time of flight of a signal. One high-accuracy time-of-flight measurement technique is taught in U.S. Pat. No. 5,983,730 (xe2x80x9cFreundxe2x80x9d), which is hereby incorporated by reference. The required degree of accuracy may be application dependent, but any economical technique of improving accuracy is generally desirable.
Freund describes a method for performing accurate time of flight measurements of acoustic signals. His and other methods may be improved by damping the acoustic transducer to shorten the acoustic signal. Various benefits may be realized by a system using a shorter acoustic signal. One of the benefits could be easier identification of the time of arrival. Because unwanted signal portions are eliminated, less processing is required to identify the time of arrival. Further, because less extraneous energy is transmitted into the system, the background noise due to echoes may be reduced. Still further, shorter pulses allow for quicker re-use of the transducer, thereby increasing the potential measurement rate of the system.
Unfortunately, existing transducer damping methods generally require additional components to dissipate the residual energy. In addition to increasing the cost, the damping components may reduce the amplitude of the transmitted signal. A solution that avoids these drawbacks would be desirable.
The problems outlined above are in large measure addressed by a device that places existing components in a damping pattern after transmitting an acoustic signal. In one embodiment, the device comprises a transistor bridge and an acoustic transducer. The transistor bridge is coupled between two predetermined voltages having a voltage difference, and the acoustic transducer is coupled between the arms of the transistor bridge. The transistor bridge enters a damping configuration after applying an excitation pattern to the acoustic transducer. In the damping configuration, the input terminals of the transistor bridge are preferably grounded. In applying the excitation pattern, the transistor bridge preferably applies the voltage difference to the acoustic transducer in alternate polarities. In a preferred embodiment, the acoustic transducer includes a transformer having a primary winding coupled between the arms of the transistor bridge, and further includes a piezoelectric crystal coupled to a secondary winding of the transformer.